code: def test_window_transformer_output(self):
      window_transformations = {
          "function": "sum",
          "components": ["0"],
      }
      transformer = WindowTransformer(
          transforms=window_transformations,
          treat_na=100,
          keep_non_transformed=True,
          forecasting_safe=True,
      )
      transformed_ts_list = transformer.transform(self.sequence_det)
  
      assert len(transformed_ts_list) == 2
      assert transformed_ts_list[0].n_components == 2
      assert (
          transformed_ts_list[0].n_timesteps
          == self.series_multi_det.n_timesteps
      )
      assert transformed_ts_list[1].n_components == 5
      assert (
          transformed_ts_list[1].n_timesteps
          == self.series_multi_det.n_timesteps
      )
  
file_path: darts/darts/tests/dataprocessing/transformers/test_window_transformations.py
imports: import itertools
  import numpy
  import pandas
  import pytest
  from darts import TimeSeries
  from darts.dataprocessing.pipeline import Pipeline
  from darts.dataprocessing.transformers import Mapper, WindowTransformer
label_desc: Use image node_id 1 for calling the TestWindowTransformer obj's underlying member method code with example usage: obj.test_window_transformer_output() without return types